1. Field of the Invention
The present invention relates to a brushless motor lock detection apparatus, and particularly to a means for notifying an external component when the motor stops turning for any reason.
2. Description of the Prior Art
The good control characteristics of recent compact DC motors have been confirmed in the audio, information processing, and various industrial fields, leading to the rapid development of applications for such motors. Brushless motors in particular have a long service life because they have no contact parts such as brushes and commutators. Industrial applications for brushless motors, for which reliability is a primary consideration, have therefore expanded rapidly.
An example of one such application is the axial-flow fan, the drive method of which has changed in recent years from AC to DC motors. DC axial-flow fans using a brushless motor are now common.
Demand for extremely high reliability DC axial-flow fans has risen steadily as the packaging density of industrial machinery, particularly computer equipment and other electronics, has increased. Demand is specifically high for fans that can prevent the motor coil from seizing when the motor stops for some external reason; can issue an alarm to the main unit of which the fan is part to prevent an accident; and can automatically reset and resume operation when the cause of the motor stoppage is removed.
The construction of a conventional drive motor for an axial flow fan is shown in FIG. 5, and comprises a magnetic detection circuit 101, position signal amplifying circuit 102, output circuit 103, and coil 104. With this configuration, if the motor is stopped by some external force or is forced to operate at a low speed due to an overload condition, the coil 104 will typically seize from the overcurrent, and the motor will cease to function. Problems such as this are prevented by interrupting the output circuit 103 by means of the circuitry described below, thus effectively blocking the overcurrent flow. More specifically, the rotation pulse generation circuit 105 comprises transistors 110 and 111 forming a differential amplifier of which the load is resistance 112; transistors 115 and 116 forming another differential amplifier of which the active load is transistors 117 and 118, which form a current mirror circuit; and transistors 113 and 119, which share the collector to which the signal from resistance 112 and transistor 118 is input. The rotation pulse generation circuit 105 emits a pulse output from the common collector synchronized to the rotational position of the rotor.
The flip-flop circuit 106 receives input from the integration control transistor 125 and inverter 129, and connects the charge-storing capacitor 122 to the constant current source 123 to charge, or to the other constant current source 124 to discharge, the capacitor 122.
The integration circuit 107 comprises resistances 126 and 127, which determine the hysteresis characteristic, comparator 128, and inverter 129. When the rotor locks and the potential of the capacitor 122 rises to potential A in FIG. 6(a), locked state protection transistor 130 is driven to interrupt the output circuit 103, and transistor 130 continues to suppress the output circuit 103 until the potential drops to C. During normal operation, the discharge transistor 121 discharges the capacitor 122 according to the pulse output from the rotation pulse generation circuit 105. When the motor locks, however, the integration circuit 107 outputs to the locked notification transistor 141, which then outputs a HIGH signal while the motor is locked.
Power is supplied from the constant current sources 109, 114, and 120.
The operation of this apparatus at this time is described below with reference to FIG. 6.
The charge and discharge states of the capacitor 122 are shown in FIG. 6(a). The rotation pulse signal is output at a regular interval of time T1 during normal operation, and the potential of the capacitor 122 does not reach the potential V.sub.OFF at which the output circuit 103 is interrupted. The motor therefore continues turning without stopping.
If for some external reason the motor stops, however, the potential of the capacitor 122 rises to point A. When the capacitor potential is equal to potential A, the integration circuit 107 operates to interrupt the output circuit 103 by means of the locked state protection transistor 130. If the capacitor potential continues to rise and reaches B, i.e., if the potential rises to V.sub.H =V.sub.ref1 +V.sub.BE (V.sub.BE is base-emitter voltage of transistor 125), the integration control transistor 125 operates, causing the contacts of the flip-flop circuit 106 to switch to the constant current source 124 to discharge the capacitor 122. The potential therefore drops to potential C. The integration circuit 107 thus works again, activating the output circuit 103 through the locked state protection transistor 130, and switching the flip-flop circuit 106 to the constant current source 123 to charge the capacitor 122. This causes the capacitor potential to rise again, and when the potential reaches point D (=A), the operation described above when the potential reaches A is repeated.
This on/off cycling of the motor during periods T3 and T4 continues until the external cause of motor stoppage is removed. If the external cause is removed during period T4, the motor is driven and the rotation pulse is emitted. This pulse drives the discharge transistor 121 to discharge the capacitor 122 and reset the normal operating mode.
The diagram in FIG. 6(b) illustrates the operation of the locked notification transistor 141 relative to the potential levels shown in FIG. 6(a). The locked notification transistor 141 outputs a HIGH signal while the rotor is locked and the locked state protection circuit interrupts the output circuit 103, and outputs a LOW signal when the locked state protection circuit releases the output circuit 103.
As described with FIG. 6(b), a HIGH signal is output when the locked state protection circuit is active, and a LOW level signal is output during period T4 when the reset pulse from the integration circuit 107 is output, but this output signal processing is complex. With respect to this problem, the present inventors proposed in Japanese patent application 2-160505 a means whereby only a HIGH (or LOW) level signal is output once the time the locked state protection circuit is activated until the cause of motor locking is remedied, thus simplifying output signal processing.
However, in addition to the method described above for emitting an alarm to an external device when the motor stops for some external reason, it is also possible to output an FG signal while the motor is turning, and not output the FG signal when the motor stops.